Prell gets rid of that stuff. I think it may have to do with the water, with all the calcium sulfate. 85% of Americans use hard water, and that stuff that gets stuck in your hair (even after you clean it), is the calcium sulfate in the water. I have the same problem. i lived in Hawaii, where the water was soft and was free of minerals, so whenever I scratched my head, i wouldn't find any calcium under my nail. But when I moved to Nevada, where the water is semi-hard, I would scratch my scalp after shampooing(regular shampoo) and see that I scraped some calcium sulfate off.
But yes, a clarifying shampoo does get rid of the calcium sulfate. I use Prell.